Field of Invention
The present invention relates to a fluid power transmission device, particularly to a fluid power transmission device for transmitting power from an engine to a transmission through a fluid.
Background Information
A torque converter equipped with a lock-up device has been well-known as an exemplary fluid power transmission device. The lock-up device is a mechanism for mechanically coupling a front cover and a turbine, and is disposed in a space produced between the front cover and the turbine.
The lock-up device includes a clutch portion and a damper mechanism. The clutch portion includes a piston having, for instance, a friction member. Now when the piston is moved and the friction member is thereby pressed onto the front cover, power is configured to be transmitted from the front cover to the damper mechanism through the piston. The damper mechanism includes a plurality of elastic members and an output-side member to which power is transmitted through the elastic members. The output-side member is fixed to the turbine.
A dynamic damper has been installed in the lock-up device with the aforementioned construction. With the installation of the dynamic damper, it is possible to reduce a peak in variation of torque to be generated at or around the resonance frequency of the damper mechanism.
As described above, one large peak in variation of torque can be inhibited with the dynamic damper. However, two peaks in variation of torque instead appear at two rotation speeds, lower than and higher than, different from the rotation speed at which the one large peak is normally supposed to appear. One of the two peaks, i.e., the peak at the low rotation speed, appears in a rotation speed range lower than a normal rotation speed range. Thus, the peak is not problematic in use of the dynamic damper. By contrast, the other of the two peaks, i.e., the peak at the high rotation speed, normally appears in the normal rotation speed range. In view of this, a device for attenuating the peak at the high rotation speed has been provided as described in Japan Patent No. 4648428 and Japan Laid-open Patent Application Publication No. JP-A-2011-58557.